JP5963202B2 - Vehicle exhaust system with "stop-start" compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust system for a compression ignition internal combustion engine of a vehicle such as a diesel engine, and more particularly to a vehicle exhaust system including a so-called engine “stop-start” system.

Prior Art In general, exhaust gases from vehicles and internal combustion engines are subject to regulations being tightened worldwide. Concerns about global warming associated with CO ₂ emissions have led to financial incentives around the world to reduce CO ₂ emissions from vehicles. Thus, private cars and light commercial vehicles, relatively fuel consumption is small, is further using lightweight diesel engine for discharging reduced relatively CO _2.

Among the plans that have been adopted to improve both fuel consumption and exhaust gas for both gasoline ignition and compression combustion (ie diesel) internal combustion engines are “stop-start”. In the case of a stop-start system, if the vehicle is stopped for more than a few seconds, the engine stops overall. When the driver needs to operate again, the action of shifting to "drive" in an automatic or semi-automatic vehicle, such as disengaging the clutch, moving the gear stick, rotating the power steering wheel, or restarting the engine Let Even if such factors further increase the load on the battery and starter motor, they need to be upgraded, which can save a lot. In testing with the New European Drive Cycle, such savings can reach up to 5% of fuel consumption and up to 8% of CO ₂ emissions by adopting a stop-start system. City authorities are worried about reducing exhaust emissions in small cities, medium and large cities, and are also focusing on reducing exhaust emissions due to traffic congestion. Therefore, many new vehicles with a stop-start system are expected to be used.

Lightweight diesel engines are even more efficient with electronic control modules and mechanically improved injection technology. This means that the temperature of the exhaust gas is much lower than in the case of gasoline engines or heavy duty (truck and bus) diesel engines. At light loads, for example “coasting” in gear in cities, little or no fuel is used by modern light duty diesel engines. Therefore, the temperature of the exhaust gas may not be as high as about 100 to 200 ° C. Despite these low temperatures, the latest catalyst technology can achieve light-off during actual urban, low-speed acceleration and normal operating conditions in the new European driving cycle. . “Light-off” may be defined as the temperature at which the catalyst catalyzes the reaction at the preferred conversion activity temperature. For example, “CO T ₈₀ ” is the temperature at which a particular catalyst converts the feed gas carbon monoxide to, for example, CO ₂ with an efficiency of at least 50%. Similarly, “HC T ₈₀ ” is the temperature at which a hydrocarbon (a specific hydrocarbon such as octane or propane) is converted to, for example, water vapor or CO ₂ with an efficiency of 80% or more.
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However, it can mean that in some circumstances, the diesel oxidation catalyst (DOC) cannot operate efficiently due to the low exhaust gas temperature. That is, the DOC may not be able to achieve or maintain “light-off”.

  For vehicles that do not have an engine “stop-start” system, additional problems caused by the operation of the engine under such light load conditions are relatively cool exhausts, mainly containing air, during engine operation. The gas is to continue to pass from the engine through the DOC or other catalyst. For example, when a load such as acceleration is reapplied, the catalyst cannot satisfy the preferred conversion rate of instant pollutant gases, and as a result, polluted exhaust gases may exceed regulatory levels for some time. . At appropriate times, the higher temperature exhaust gas will once again raise the catalyst temperature above the light-off temperature.

A DOC structure comprising a flow-through monolith comprising first, second and third platinum group metal containing washcoat zones (numbered in order from upstream to downstream) is disclosed in WO 2007/077462. The platinum group metal content in each of the first and third zones is even higher in the second zone, which is spatially located between the first zone and the third zone. The third zone, the zone furthest away from the engine when in use, utilizes a washcoat material having an essentially higher heat (quality) quantity, such as a thicker washcoat or dense zirconia, for example. Thus, a washcoat having a higher thermal mass than the first and second zones can be included. High density zirconia can have a density of 3.5 g / cm ³ . The three zone arrangement is designed to maintain catalyst performance with overall reduced platinum group metal costs.

Compared to conventional diesel engines that maintain operation in the idle state, the catalyst is not cooled by contact with the relatively cool exhaust gas in the idle state, so vehicle diesel engines equipped with “stop / start” technology The change in the catalyst temperature is generally small over the operation cycle. The inventors of the present invention have devised a diesel oxidation catalyst with improved activity for the treatment of exhaust gas emitted from diesel vehicles equipped with such “stop / start” technology. In particular, the inventors have determined that the competitive requirement for low catalyst light-off temperature to treat cold-start exhaust gas as fast as possible and that the catalyst is already “light” after cold-start. A device was devised that balances “light-out” after “light-off” and below the desired activity during the cold period of the driving cycle.

SUMMARY OF THE INVENTION The present invention provides a vehicle comprising a compression ignition internal combustion engine having engine management means and a catalyst for exhaust gas aftertreatment, wherein the engine management means detects idle conditions during use and Determining the presence and shutting down the engine as a whole, the catalyst comprising a honeycomb substrate monolith coated with a catalyst washcoat comprising one or more precious metals, the catalyst washcoat comprising a first upstream washcoat area and a first Between the second downstream washcoat zone, the thermal mass of the first washcoat zone is different from the thermal mass of the second washcoat zone, and the washcoat layer of the first upstream washcoat zone Is substantially continuous with the washcoat layer in the second downstream washcoat area.
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A suitable compression ignition internal combustion engine uses diesel fuel, but other forms of fuel are possible including a mixture of natural gas (NG) and diesel and biofuel or a Fischer-Tropsch process induction fuel.
[11]
The honeycomb substrate monolith may be made of a ceramic material such as cordierite or silicon carbide or a metal such as Fecralloy. Such a device is preferably of a so-called flow-through configuration, in which a number of channels extend in parallel from the open inlet end to the open outlet end. However, the honeycomb substrate monolith may also take the form of a filtering substrate such as a so-called wall-flow filter or ceramic foam.

  In one embodiment, the thermal mass of the first upstream washcoat zone is greater than the thermal mass of the second downstream washcoat zone. However, in a preferred embodiment here, the thermal mass in the first upstream washcoat zone is less than the thermal mass in the second downstream washcoat zone.

  In one of the embodiments, the honeycomb substrate monolith has a full length. In an embodiment, the first upstream washcoat area is 15% to 80% of the total length of the substrate monolith measured from the upstream end at the inlet end of the honeycomb substrate monolith and the inlet end. Defined at the downstream end at a point between 10% and 90%, such as between (for example, between 20% and 30% or between 20% and 40%). In a preferred embodiment, the length of the inlet area is smaller than the outlet area.

  A preferred feature of a low washcoat content is that its relatively low thermal mass heats up more quickly, thereby enabling more efficient “light-off” following a cold start. However, due to the low thermal mass, the catalyst can also be cooled more quickly, and in this connection “light-out” in the middle of the operating cycle (ie post- “light-off”) after initial warm-up. "Is not preferable. The higher washcoat content has the advantage that more support material is present in the supported noble metal and higher noble metal dispersion is possible. A higher washcoat content can provide greater resistance to thermal aging, ie higher thermal durability, in use.

In certain embodiments, for each of the second or first zones, other thermal mass in the first or second zone is provided by a thicker washcoat layer than is used in other zones. The In such embodiments, the washcoat content in the thicker washcoat layer is 0.2-0.6 gcm ⁻³ (4 , such as 0.3-0.5 gcm ⁻³ (5-8 gin ⁻³ ). 10 gin ⁻³ ) . On the other hand, the content of the washcoat in the thinner washcoat layer is 0.06-0.21 gcm , such as 0.1-0.2 gcm ⁻³ (2-3 gin ⁻³ ) , relative to other areas. ^-3 (1-3.5 gin ^-3 ) .

In contrast, according to another embodiment, a wash having a density of at least 3.50 gcm ⁻³ , which is another thermal mass in said first or second zone for each of the second or first zone. It can be provided by a coating component. A material having a suitable density may be selected from the group consisting of high density alpha alumina, high density lanthanum oxide, high density cerium II oxide, high density cerium III oxide and high density zirconia.

  In a preferred embodiment, the precious metal content in the second downstream washcoat area is measured in unit mass of precious metal per unit volume of washcoat in the first upstream washcoat area. More than the whole.

In one embodiment, for example, the first upstream washcoat zone comprises 55-9 0% of the total content of noble metal honeycomb substrate monolith. In other embodiments, the first upstream washcoat zone comprises 60-80% of the total precious metal content of the honeycomb substrate monolith.

The total content of the noble metal on the honeycomb substrate monolith is 1.1 to 5.3 kgm ⁻³ (30 to 150 gft ⁻³ ) (for example, 1.4 to 4.2 kgm ⁻³ (40 to 120 gft ⁻³ ) ). Such as 0.53 to 11 kgm ⁻³ (15 to 300 gft ⁻³ ) .

  The noble metals for use in the present invention include one or more selected from platinum, palladium, rhodium, gold, silver or mixtures of two or more thereof. A subset of preferred embodiments of noble metals for use in the present invention are platinum group metals.

Particularly suitable noble metal selections are platinum, palladium, platinum and palladium mixtures (optionally present as an alloy) or combinations and mixtures of palladium and gold , including both alloys or mixtures and alloys.

  In certain embodiments, the noble metal or noble metal combination in the first upstream zone is different from the noble metal or noble metal combination in the second upstream zone.

  In general, the noble metal is supported on a high surface area refractory oxide component. Suitable noble metal support components include molecules, mixtures, complex oxides such as alumina, silica, amorphous aluminosilicate, aluminosilicate zeolite, titania, magnesia, magnesium, aluminate, cerium oxide, zirconia and the like. Of these, two or more mixed oxides, optionally those stabilized with one or more rare earth components. Particularly suitable mixed oxides include cerium oxide-zirconia, which may also include alumina doped with one or more rare earth metals and silica (depending on the content of cerium oxide).

  The catalyst for use in the present invention may be located at an appropriate location in the vehicle taking into account packaging and vehicle spatial limitations. A common location is an adjacent coupling location located as close to the engine exhaust manifold as possible, with the advantage of the hottest exhaust gas temperature. Another common location is the so-called “underfloor” location.

  In order that the present invention may be more fully understood, the following embodiments are provided for purposes of illustration only with reference to the accompanying drawings.

  FIG. 1 shows computer modeled mass flow, adjacent coupled DOC inlet temperature, exhaust gas carbon monoxide and hydrocarbons in a 2.4 liter Euro IV bench-mounted vehicle diesel engine over the MVEG-B European driving cycle over time. It is the graph which compared.

FIG. 1 is a graph comparing mass flow, inlet temperature of adjacent bonded DOC, exhaust gas carbon monoxide and hydrocarbons.

Embodiment The following embodiment shows the results of a computer model where a cordierite flow-through honeycomb monolith substrate having a size of 143 × 98 × 135 mm of cylindrical 400 cells per square inch and a volume of 1.50 L is shown. Of low ( 0.15 gcm ⁻³ (2.5 gin ⁻³ ) ) or high ( 0.43 gcm ⁻³ (7.0 gin ⁻³ ) ) and uniform platinum content (comparative example) Coated with a homogeneous diesel oxidation catalyst washcoat layer. The zoned diesel oxidation catalyst according to the present invention is manufactured using the same bare honeycomb substrate monolith and is shown in Table 1.

  A method of manufacturing a zoned honeycomb substrate monolith has been presented in the technical field of the present invention and includes WO 99/47260 filed by the applicant of the present invention, ie, the method comprises (a) Positioning the sealing means on top of the support, (b) providing a pre-set amount of liquid component to the sealing means (the order of (a) and (b) may vary) and (c) pressure And / or creating a vacuum to draw the liquid component onto at least a portion of the support to substantially maintain the entire amount within the support.

The percentage figures shown in the “Washcoat Content” column of Table 1 are the first upstream zone (leftmost column) and the second downstream zone relative to the total length of the substrate measured from the inlet end of the substrate monolith. Indicates the length. The “Pt content” column shows the platinum content in the first upstream zone (left column) and the second downstream zone, respectively, from left to right. The figures for CO (g) and HC (g) are for carbon monoxide and hydrocarbons measured at the outlet of the diesel oxidation catalyst. "Standardized CO (g) conversion rate" and "standardized HC (g) conversion rate" are low washcoat contents ( 1.4 kgm- ³ (40 gft- ³ ) ) uniformly coated (comparative example) To 2). In all embodiments, the overall platinum content was constant.

  Mass flow rate, temperature and total content of engine-out carbon monoxide (CO (g)) and hydrocarbons (HC (g)) of exhaust gas from 2.4 liter Euro IV bench mounting vehicle diesel engine (given) Recorded using a vehicle dynamometer mounted in the so-called adjacent coupling position, located as close as possible to the engine's exhaust manifold (with limited spatial constraints), and such data is recorded using a modeled catalyst structure. Used to implement a computer model. Even if the engine used is not equipped with “stop-start” technology, the effect of such a system was mimicked by stopping the engine every time the MVEG-B Europian driving cycle reached idle. . Mass flow rate, catalyst inlet temperature, exhaust gas carbon monoxide (CO) and total hydrocarbons (THC) are shown in FIG.

The results are shown in Table 1, but instead of using a uniform low washcoat content (Comparative Embodiment 2), the use of a uniform high washcoat content (Comparative Embodiment 1) is now MVEG-B. It can be seen that the CO and HC conversion is reduced over the entire cycle. This can be seen because the increased thermal mass of the catalyst causes the catalyst to arrive later at light-off for CO and HC conversion at the start of the test.

  When the upstream half of the substrate monolith is coated with a low washcoat content and the downstream half remains coated with a high washcoat content (Embodiment 3), the relative platinum metal content between the zones CO oxidation was improved without adjusting the amount. For the tested vehicle, the reverse arrangement of such a configuration (upstream 50% is high washcoat content and downstream half is low washcoat content (ie Embodiment 4)) is controlled. The activity is even worse. However, the tested vehicle is particularly equipped with a cold-running engine, and the inventor has found that the engine of Embodiment 4 operates at a higher temperature (the product offered by other vehicle manufacturers is MVEG-B on-cycle exhaust gas It is believed that this can be particularly useful in vehicles with (which may vary in temperature). Therefore, the structure of Embodiment 4 is judged to belong to the scope of the present invention. However, the results of the remainder of Table 1 (ie, embodiments 5-8) relate to configurations having a low content upstream zone, but varying the length of the upstream zone and the platinum metal content.

  By reducing the length of the upstream low washcoat content area to 25% (Embodiment 5), the structure of Embodiment 4 is further improved in CO oxidation. The remaining embodiments (embodiments 6-8) maintain an array of 25% long inlet zone low washcoat content / 75% long outlet zone high washcoat content, and between the two zones Changes in the distribution of platinum metal content were investigated.

Low ( 0.71 kg / m ³ (20 g / ft ³ ) ) compared to the platinum content in the outlet area High ( 3.5 kg / m ³ (100 g / ft ³ ) ) The platinum content in the inlet area is the CO conversion rate However, the HC conversion rate was slightly reduced as compared with the uniform content embodiment (see the results in Table 1 for Embodiment 6). However, platinum distribution 2.5 kg / m ³ (70 g / ft ³ ) upstream zone / 1.1 kg / m ³ (30 g / ft ³ ) downstream zone (Embodiment 7) and 3.0 kg / m ³ (85 g / ft ³ ) ³ ) Additional iterations of upstream zone / 0.88 kg / m ³ (25 g / ft ³ ) downstream zone (Embodiment 8)) provide similar HC conversion rates for homogeneous content catalysts. Surprisingly, the CO conversion was improved compared to the high PGM content upstream zone embodiment (ie, the 3.5 kg / m ³ (100 g / ft ³ ) upstream zone embodiment).

  To eliminate any doubt, the entire contents of the documents cited herein are included here as a reference.

Claims (11)

A vehicle comprising a compression ignition internal combustion engine having an engine management means and an exhaust gas aftertreatment catalyst,
The engine management means is configured to detect idle conditions during use, determine the existence of idle conditions, and stop the engine as a whole.
The catalyst comprises a honeycomb substrate monolith coated with a catalyst washcoat comprising one or more precious metals;
The catalyst washcoat extends from the upstream washcoat zone to the downstream washcoat zone;
The washcoat layer on the upstream side washcoat zone is intended to continue communication with the washcoat layer in the downstream washcoat zones,
The thermal mass in the upstream washcoat zone is less than the thermal mass in the downstream washcoat zone,
The precious metal content in the upstream washcoat zone is 55-90% of the total precious metal content of the honeycomb substrate monolith ,
The honeycomb substrate monolith has a full length,
The upstream washcoat zone is defined by an upstream end by the inlet end of the honeycomb substrate monolith, and is 20% to 40% of the total length of the honeycomb substrate monolith measured from the inlet end. A vehicle having a downstream end defined by a point in between . A greater thermal mass in the downstream washcoat zone than in the upstream washcoat zone is provided by a thicker washcoat layer in the downstream washcoat zone than in the upstream washcoat zone. The vehicle according to claim 1 . The vehicle according to claim 2 , wherein the thicker washcoat layer is applied at a washcoat content of 0.2 to 0.6 gcm ⁻³ (4 to 10 gin ⁻³ ) . The upstream washcoat zone has a thinner washcoat layer than the downstream washcoat zone, and the thinner washcoat layer is 0.06-0.21 gcm- ³ (1-3.5 gin- ³ ) washcoat. The vehicle according to claim 2 or 3 , comprising a content. Wherein the downstream washcoat zones, larger thermal mass compared to the upstream washcoat zone, formed by applying a washcoat component having a density of at least 3.50Gcm ^-3, vehicle according to claim 1. The washcoat component, A Alpha alumina, La Ntana, Se helium II oxide, formed by selected from the group consisting of Se potassium III oxide及beauty di zirconia, vehicle according to claim 5. The vehicle according to any one of claims 1 to 6 , wherein a content of the noble metal in the upstream washcoat area is 60 to 80% of a total content of the noble metal of the honeycomb substrate monolith. Total content of noble metal in the honeycomb substrate monolith to volume of the honeycomb substrate monolith is a 0.53~11kgm ^-3 (15~300gft ^-3), according to any one of claims 1 to 7 Vehicle. The vehicle according to any one of claims 1 to 8 , wherein the one or more noble metals are selected from the group consisting of platinum, palladium, rhodium, gold, silver, and a mixture of two or more thereof. The vehicle according to claim 9 , wherein the noble metal is platinum, palladium, a mixture of platinum and palladium, or a combination of palladium and gold. The vehicle according to claim 9 or 10 , wherein the noble metal or combination of noble metals in the upstream washcoat zone is different from the noble metal or combination of noble metals in the downstream washcoat zone.

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